The pushbutton of the invention is suitable for fitting onto the rod of a valve which is preferably a metering valve and which, at rest, closes the receptacle of various kinds of spray device while enabling the valve rod to be pushed in a little merely by applying finger pressure so as to allow the substance contained in the receptacle to escape (which substance is referred to below as the primary substance). In addition to stopping and starting emission of the primary substance, the pushbutton of the invention has the special feature of mixing a predetermined quantity of another substance (referred to below as the secondary substance) with the primary substance, with said mixing taking place as the primary substance is being emitted. That is why the name "exomix" has been applied to this pushbutton. It is particularly suitable for the pharmaceutical industry in which medicines to be sprayed may comprise a basic substance, perhaps a solvent, together with an additive, perhaps a solute, e.g. two liquids or a liquid and a powder, which are unsuitable for being put into contact with each other a long time in advance of being used. Utilization of such a mixing pushbutton also forms part of the present invention.
A pushbutton capable of performing such mixing exists in the prior art. It is described in French patent number FR-A-1 506 698 filed in 1966 by Marraffino. It comprises a hollow cylinder terminated by a protection which serves simultaneously as the emission channel and as the member, for actuating the valve of the spray device. A chamber is disposed around said cylinder and is in communication therewith via at least one bottom orifice, and the user may place a supply of hot water in said chamber. At rest, the water penetrates via the orifice into the bottom of the emission channel. By pressing down the hollow cylinder, the user may release, for example, shaving foam which is heated up by entraining and mixing with the water in the emission channel.
However, this prior art system is not suitable for spraying mixtures of medicines. It is often necessary for the various components of such mixtures to be protected from contact with air until the moment they are applied. There can thus be no question of placing one of these components (the "secondary" substance) in a chamber which is permanently in communication with the emission channel since the emission channel is generally open to the outside. Further, therapeutic use of such substances normally requires them to be used in carefully measured doses. Unfortunately, the pushbutton described above mixes ever smaller quantities of water in the shaving foam it emits as the supply in the chamber is used up. These two major reasons therefore require the Marraffino pushbutton to be rejected and require a new pushbutton to be developed in which the supply of the secondary substance is firstly sheltered from contact with air, and is secondly present in a known volume which is predetermined as a function of requirements.